The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
The present disclosure pertains to a blood filtering device and a method for the recuperation of blood from wound drained blood, in particular for an autologous blood transfusion and a system therefor, the filtering device comprising an entrance port for the blood, a first filter and a second filter, wherein the first filter is arranged upstream of the second filter, the first filter adapted for removing emboli and/or large particulate matter from the blood received through the entrance port and for allowing red blood cells to pass, the second filter adapted for retaining red blood cells and an exit port arranged between the first and second filter, i.e. downstream of the first filter and upstream of the second filter.
After a patient has undergone an operation, specific wounds, e.g. thorax wounds after cardiac operations, may be provided with drains to remove the wound secretions, which fluid usually comprises blood. A patient may lose so much blood that he/she requires a blood transfusion. Autologous blood transfusion, the reinfusion of a patients own blood, minimises risks linked to blood transfusions with blood donated by other people, so-called homologous blood transfusions, viz. anaphylactic reactions and/or donor-associated infections such as hepatitis, acquired immune deficiency syndrome (AIDS), adverse effects HLA (human leucocytes antigens), and malaria.
For an autologous blood transfusion, the fluid comprising the lost blood must be collected and the blood to be reinfused must be recuperated therefrom. This blood which preferably is as rich as possible in healthy red blood cells or erythrocytes, must be filtered out of the drained blood and freed or washed from impurities and/or contaminants before reinfusion. Typical impurities in blood drained from a recovering wound site are, among others, bone and tissue fragments, blood clots and fat particles, as well as activated coagulation factors, plasma free haemoglobin, denaturated proteins, platelets, leucocytes and lipids.
The purification of autologous blood, generally called “washing”, is usually performed in two steps: first the drained fluid is filtered relatively coarsely to remove large particulate debris and impurities from the blood, next the filtrate is mixed with a “washing fluid”, usually a saline solution or Ringer's solution, put in a centrifuge chamber for separation of the relatively heavy blood cells from the blood plasma and relatively light and small particles such as platelets, plasma proteins and antibodies. The recovered blood is generally reinfused under low pressure through a leukocyte filter for further reducing the number of remaining white blood cells in the transfused blood.
This cell washing technique works only for batches. Further, during washing by the centrifuge-process, significant numbers of the collected red blood cells become damaged and are lost to the patient. This method depends on complex equipment that is not available when the blood loss is over an extended period of time, e.g. 6-12 hours, on a non operating room such as an Intensive Care Unit (ICU).
An improvement to this technique is provided by using a two-step filtering system which may be used for continuous or quasi-continuous washing of wound drained blood. Such a filter system is known from EP 0 518 975, which discloses an apparatus for recycling autologous blood from a patient for reinfusion back to the patient comprising suction means, admixing means for admixing aspirated blood with a washing fluid, filtering means for filtering the admixture through an emboli filter and a membrane filter, monitoring means for measuring the amount of cellular component volume in the filtered blood, filtration means for removing excess fluid and particulates from the blood, and reinfusion means. The membrane filter may be any conventional membrane-type separator with a pore-size ranging from 40 000 daltons to 400 000 daltons molecular weight cut-off. However, if larger impurities are to be removed, a plasma filter having a pore size larger than about 400 000 daltons, and up to 0.4 μm, can be used.
In order to achieve filtering of the blood from small impurities through such commercially available membrane filters, experiments have proven that only blood having a blood cellular volume, or haematocrit, of less than about 25% and an applied pressure difference across the membrane filter of more than about 400 mm Hg should be used. Furthermore, the filters tend to clog, requiring an even higher pressure difference and/or an even lower haematocrit for operation. These devices can also work only if strong anticoagulation by medication such as heparin is used during filtering.
It is desired, in particular for severely weakened patients such as those stationed on an intensive care ward, to have a simple, reliable filtering device which may yield purified blood with a high haematocrit value, e.g. 70% or even higher, for autologous blood transfusions. This will enhance recovery of the patient and reduce morbidity and mortality.
Further, systems capable of reaching the necessary relatively high pressure difference, i.e. moderate to high vacuum sources or roller pumps may be unavailable in some hospitals, especially in less-developed countries.
Moreover, it has become apparent that the autologous blood prepared according to the prior art may still comprise impurities such as fractured red blood cells, activated platelets or activated tissue factors, which may cause complications to the patient such as inflammation reactions.
An improved blood filtering device and a method, for the recuperation of blood from wound drained blood is always desired.